1. Field of the Invention
This invention relates generally to internal combustion engine ignition systems and, in particular, to ignition systems with an ignition coil.
2. Prior Art
U.S. Pat. No. 3,938,490 discloses an ignition control circuit having an open secondary protective circuit for preventing open circuits in the secondary winding from destroying portions of the ignition system. The patent discloses an open secondary Zener clamp protection circuit, two induction emission systems, and teaches using the coil flyback voltage in order to regulate the primary circuit coil voltage. An open secondary sensor includes a voltage divider network but does not detect a reverse current in the primary for generating a signal indicating an open secondary circuit.
U.S. Pat. No. 4,153,032 teaches sensing current, but not the reverse current in the primary of an ignition circuit, and then comparing the sensed current or voltage with a reference value to control emission. However, there is no open secondary detection performed by the sensing resistor or the comparator. That is, the primary circuit sense resistor is used to control coil energy. The patent teaches only using the sense resistor link conducting current as in the forward direction. There is no teaching of open secondary detection.
Various other patent references are also generally related to the operation of ignition coils within ignition systems.
U.S. Pat. No. 4,114,582 teaches a secondary protection system circuit utilizing a high voltage connection to the secondary circuit.
U.S. Pat. No. 4,117,819 teaches using engine rotation speed information in order to regulate the percent dwell applied to the ignition system. There is no teaching of open secondary detection.
U.S. Pat. No. 4,359,038 teaches a primary coil drive in the clamp circuit which may be incorporated into an introverted circuit to eliminate the need for an external Zener clamp for protection. Open secondary detection is not mentioned.
GB No. 2 060 053 A, providing primary current overload protection by using a forward current through a sense resistor. Again, open secondary detection is not mentioned.